linux-kernel - [PATCH 6/7] selinux: Ignore security labels on user namespace mounts

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Message-Id: <1436989569-69582-7-git-send-email-seth.forshee@canonical.com>
Date:	Wed, 15 Jul 2015 14:46:07 -0500
From:	Seth Forshee <seth.forshee@...onical.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Paul Moore <paul@...l-moore.com>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	Eric Paris <eparis@...isplace.org>
Cc:	Serge Hallyn <serge.hallyn@...onical.com>,
	Andy Lutomirski <luto@...capital.net>,
	Seth Forshee <seth.forshee@...onical.com>,
	linux-fsdevel@...r.kernel.org,
	linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-kernel@...r.kernel.org,
	James Morris <james.l.morris@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>
Subject: [PATCH 6/7] selinux: Ignore security labels on user namespace mounts

Unprivileged users should not be able to supply security labels
in filesystems, nor should they be able to supply security
contexts in unprivileged mounts. For any mount where s_user_ns is
not init_user_ns, force the use of SECURITY_FS_USE_NONE behavior
and return EPERM if any contexts are supplied in the mount
options.

Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
---
 security/selinux/hooks.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 459e71ddbc9d..eeb71e45ab82 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -732,6 +732,19 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 	    !strcmp(sb->s_type->name, "pstore"))
 		sbsec->flags |= SE_SBGENFS;
 
+	/*
+	 * If this is a user namespace mount, no contexts are allowed
+	 * on the command line and security labels mus be ignored.
+	 */
+	if (sb->s_user_ns != &init_user_ns) {
+		if (context_sid || fscontext_sid || rootcontext_sid ||
+		    defcontext_sid)
+			return -EPERM;
+		sbsec->behavior = SECURITY_FS_USE_NONE;
+		goto out_set_opts;
+	}
+
+
 	if (!sbsec->behavior) {
 		/*
 		 * Determine the labeling behavior to use for this
@@ -813,6 +826,7 @@ static int selinux_set_mnt_opts(struct super_block *sb,
 		sbsec->def_sid = defcontext_sid;
 	}
 
+out_set_opts:
 	rc = sb_finish_set_opts(sb);
 out:
 	mutex_unlock(&sbsec->lock);
-- 
1.9.1

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